线程池示例代码，请大家多指教

package com.shy.sql;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.Hashtable;

public class QConnectionPool {
	private Hashtable connections;// 连接列表
	private int increment;// 连接增长量
	private String dbURL;// 数据库连接url
	private String user;
	private String password;
	private String diverClassName;// 驱动名称
	/**
	 * 构造方法
	 * 
	 * @param dbURL
	 *            数据库连接url
	 * @param user
	 *            用户名
	 * @param password
	 *            密码
	 * @param driverClassName
	 *            驱动名称
	 * @param initialConnections
	 *            初始连接数
	 * @param increment
	 *            增加数
	 * @throws SQLException
	 * @throws ClassNotFoundException
	 */
	public QConnectionPool(String dbURL, String user, String password,
			String driverClassName, int initialConnections, int increment)
			throws SQLException, ClassNotFoundException {
		Class.forName(driverClassName);
		this.dbURL = dbURL;
		this.user = user;
		this.password = password;
		this.increment = increment;
		connections = new Hashtable();
		for (int i = 0; i < initialConnections; i++) {
			connections.put(DriverManager.getConnection(dbURL, user, password),
					false);
		}
	}

	/**
	 * 从连接池返回一个Connection
	 * @return
	 * @throws SQLException
	 */
	public Connection getConnection() throws SQLException {
		Connection conn = null;
		Enumeration conns = connections.keys();
		synchronized (connections) {
			while (conns.hasMoreElements()) {
				conn = (Connection) conns.nextElement();
				Boolean b = (Boolean) connections.get(conn);
				//如果是不使用的连接，使其使用
				if (b == Boolean.FALSE) {
					try {
						conn.setAutoCommit(true);
					} catch (SQLException e) {
						connections.remove(conn);
						conn = DriverManager.getConnection(dbURL, user,
								password);
					}
					// 更新Hashtable
					connections.put(conn, Boolean.TRUE);

					return conn;
				}
			}
		}

		//如果没有空闲的连接，增加连接数
		for (int i = 0; i < increment; i++) {
			connections.put(DriverManager.getConnection(dbURL, user, password),
					Boolean.TRUE);
		}
		return getConnection();
	}
	
	/**
	 * 由连接池客户用来向连接池返回一个Connection
	 */
	public void returnConnection(Connection returned){
		if(connections.containsKey(returned)) {
			connections.put(returned, Boolean.FALSE);
		}
	}
}